Air dryer in a wind power station

ABSTRACT

The invention relates to an air dryer in a wind power station comprising a frequency converter with liquid cooling, the air dryer comprising a Peltier element ( 3 ), the first side of which is connected to an element to be cooled ( 1 ) and the second side to a heat-receiving element ( 2 ), and while the element to be cooled ( 1 ) is cooled, humidity condenses on the surface of this element. The air dryer is located inside a frequency converter cabinet and the heat-receiving element ( 2 ) of the air dryer is connected to contact piping ( 4 ) for liquid cooling or formed as a part of the piping. The invention also relates to a method for using such an air dryer.

BACKGROUND OF THE INVENTION

The invention relates to an air dryer in a wind power station comprisinga frequency converter with liquid cooling, the air dryer comprising aPeltier element, the first side of which is connected to an element tobe cooled and the second side to a heat-receiving element, and while theelement to be cooled is cooled, humidity condenses on the surface ofthis element. The invention also relates to a method for using such anair dryer.

In wind power stations, frequency converters are located either in thelower part of the tower or in a room which is not typically heated orair-conditioned. Wind power station electronics are cooled in smallerdevices of less than 2 MW usually by outside air, but in bigger devicesthe volume of air becomes so large that liquid cooling must be adopted,by which dissipation power can be conveniently transferred out of thetower.

When it is foggy, air absorbed by cooled devices is moist, wherefore themoisture resistance of the devices should be good. In air-cooleddevices, salt can also enter inside the devices. If entirely closeddevices were manufactured and heat was transferred away by means of aliquid, this would have great benefits also in corrosion prevention.

A fully sealed device cannot, however, be manufactured with reasonablecosts. An example of a small-scale application is an air-sealed package,inside of which there is a bag containing a substance absorbing humidityfrom air. As an alternative for the bag, the device could be closed inentirely dry conditions, but this is often difficult to implement, sincereally dry air is required, for instance, to prevent humidity fromcondensing in the device during transportation, which immediately causesproblems.

Also, delivered devices are usually opened, so even though the devicewould be entirely air-proof and air-sealed, air tightness disappearsimmediately when the device is opened.

A previous air drying method in connection with wind power stations isknown from publication DE 102 45 103 A1, wherein an electronics cabinetof a wind power station is dried by using a Peltier element. Air isblown via the hot side of the Peltier system and the heated air istransferred to electrical instruments, whereby the hot air bindsmoisture in itself and flows then to the cold side of the Peltiersystem, where the humidity condenses and flows finally along a channelout of the device cabinet as condensate water.

Another known solution is shown in publication U.S. 2005/0002787 A1,which also uses the Peltier system either with or without blowers andwherein as a result of air circulation, humidity condenses on the coldside of the Peltier system. In this implementation, either the entireinterior of the wind power station or its engine room is dried, and thecondensate water is guided out of a collecting container. In animplementation, the heat-receiving side of the Peltier system isconnected to a wall of the wind power station tower or formed by thetower wall itself.

Publication JP 2003 93829 describes an air dryer utilizing a Peltierelement but no blower. Air flow is produced in channels for hot and coldair by the gravity.

In the previous solutions, it is typical that the entire interior of awind power station or at least a large part of the interior is kept dry,whereby it is assumed that electricity consumed by the dryer isavailable all the time.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide efficient and rapidlocal dehumidification in the previously mentioned wind power station.This is achieved by a solution of the invention, which is characterizedin that the air dryer is located inside a frequency converter cabinetand that the heat-receiving element of the air dryer is connected tocontact piping for liquid cooling or formed as a part of the piping.

The method of the invention is characterized by what is disclosed in thecharacterizing part of claim 6.

Since drying in the present invention is carried out locally only insidethe frequency converter cabinet, if needed, drying is very rapid and itdoes not require much electricity.

Drying may be started even after a fairly long shutdown in a totally wetspace without pre-drying, because the dryer itself is entirely resistantto condensate water.

Energy is only used during drying, and thus energy is consumed much lessthan in previous systems with continuous drying. Drying is only neededif the frequency converter cabinet becomes damp in special cases,because normally heat losses of the frequency converter are enough tokeep humidity absent.

The structure of the dryer is simple and reliable, because it does notinclude movable parts, such as blowers of prior art devices.

LIST OF FIGURES

The invention will now be described in greater detail with preferredexamples and with reference to the attached drawings, in which

FIG. 1 shows an air dryer of the invention; and

FIG. 2 shows a second air dryer of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an air dryer of the invention, consisting of a Peltiersystem with an element to be cooled 1, such as a cooling rib set, aheat-receiving element 2 and a Peltier element 3 therebetween, which,during its operation, cools down the element 1 and transfers heat fromit to the element 2.

The air dryer is located inside a frequency converter cabinet (notshown) of a wind power station, the cabinet being cooled with liquidcooling. The heat-receiving element 2 is attached to the surface of amain water pipe 4 for liquid cooling, to which heat produced in thePeltier element 3 is transferred by means of said element 2. The element1 is cooled to a dew temperature, at which air humidity condenses on thesurface of the element 1.

Under the element 1 there is a channel 5, in which the condensate wateris collected. From the channel 5 the water is then drained out of thecabinet in a controlled manner.

The use of the air dryer is controlled most preferably by a condensatewater sensor 6, which may be located in the channel 5 or, for instance,in the part of the apparatus that dries most slowly or is the mostsensitive to condensate water. A suitable direct-current supply isarranged for the use.

Other useful implementations for controlling the operation could be

-   -   an arrangement based on a temperature difference between outside        and inside air, for instance, or between some components and the        cold surface of the air dryer    -   an arrangement based on relative humidity, which is the most        common application in previous heating arrangements    -   an arrangement based on relative humidity and temperatures    -   a dew point sensor (preset air is always kept above a certain        temperature, the dew point below it)    -   an arrangement based on a dew point sensor and temperatures.

When the temperature of the device is always kept above a certaintemperature, such as at +10 degrees, in some manner, e.g. by athermostat, the dew point sensor may be used for measuring whether thedew point is below this temperature, in which case the device isprobably dry. When the temperature is measured, no preset temperature isrequired. In practice, one dew point sensor and a plurality oftemperature measurements could be employed, but this is, however, notvery likely, since dew point sensors are still quite expensive.

All the above operation controls of the air dryer tend to measure thesame thing but with different approaches. In principle, the easiest wayis to use an arrangement based on temperature differences, but it iscumbersome to measure the temperature of a dryer surface, because, ifthe surface is wet all the time, it either gets dirty or organic growthdevelops on it, which complicates the prediction of the surfacetemperature, i.e. the dew point.

When relative humidity is measured, it must be measured in a pluralityof places or a dew point temperature must be calculated on the basis ofit, since temperatures and humidity may vary greatly between the upperand lower parts of the cabinet. Like cheap thermometers, a cheapindicator for relative humidity may be based, for instance, on bi metalstrips.

The implementation shown in FIG. 2 differs from the solution accordingto FIG. 1 in that the heat-receiving element 2 is arranged in connectionwith piping 7 branched off the main water pipe 4. The piping 7 may thenbe guided through the element 2, as shown in FIG. 2. In principle, it isalso possible that part of the piping 7 forms the element 2 itself.

The above description of the invention is only intended to illustratethe basic idea of the invention. A person skilled in the art may,however, modify its details within the attached claims.

1. An air dryer in a wind power station comprising a frequency converterwith liquid cooling, the air dryer comprising a Peltier element, thefirst side of which is connected to an element to be cooled and thesecond side to a heat-receiving element, and while the element to becooled is cooled, humidity condenses on the surface of this element,wherein the air dryer is located inside a frequency converter cabinetand that the heat-receiving element of the air dryer is connected tocontact piping for liquid cooling or formed as a part of the piping. 2.An air dryer as claimed in claim 1, wherein the heat-receiving elementof the air dryer is connected to a surface of a main water pipe.
 3. Anair dryer as claimed in claim 1, wherein the heat-receiving element ofthe air dryer is arranged in connection with the piping branched off themain water pipe.
 4. An air dryer as claimed in claim 1, wherein theoperating energy of the air dryer is direct current.
 5. An air dryer asclaimed in claim 1, wherein the operation control of the air dryer isimplemented by means of a condensate water sensor.
 6. A method fordrying air in a wind power station comprising a frequency converter withliquid cooling, wherein the drying is carried out by an air dryercomprising a Peltier element, the first side of which is connected to anelement to be cooled and the second side to a heat-receiving element,and while the element to be cooled is cooled, humidity condenses on thesurface of this element, by locating the air dryer inside a frequencyconverter cabinet, connecting the heat-receiving element of the airdryer to contact piping for liquid cooling or forming it as a part ofthe piping, and carrying out the drying only if necessary, withoutpre-drying.
 7. A method as claimed in claim 6, by controlling the dryingby means of a condensate water sensor.